Filter insert for an electrical connector assembly

ABSTRACT

A filter insert for a terminal connector includes a rigid substrate and low-cost interference fit connections between the filter insert circuitry and the connector terminals. In a first embodiment, the insert includes a flexible circuit bonded to the rigid substrate, and the substrate is provided with over-sized openings that the terminals pass through without interference. A second embodiment is like the first, except that the filter circuit traces are formed directly on the rigid substrate, and the substrate material backing the terminal connection sites is removed to form the over-sized openings.

TECHNICAL FIELD

The present invention relates to an electrical connector assembly, andmore particularly to a filter insert that is electrically coupled to theconnector terminals for filtering electrical signals carried by theterminals.

BACKGROUND OF THE INVENTION

Most electronic modules include a connector assembly for coupling themodule to power supplies and external components such as sensors andactuators. Referring to FIG. 1A, a typical connector assembly 10includes a matrix of terminals 12 supported in an insulator block 14that passes through a wall of the module housing 16. The inboard ends ofthe terminals 12 are electrically coupled to a circuit board 18 enclosedby the module housing 16, while the outboard ends of the terminals 12are accessible for electrical interconnection with a complementaryconnector and electrical cable (not shown). A filter insert 20 disposedbetween the insulator block 14 and the circuit board 18 is electricallycoupled to the terminals 12, and includes filter elements such ascapacitors for filtering electrical signals carried by the terminals 12.In many applications, such filtering is necessary in order to attenuateunwanted electrical noise as well as to reduce radiated electromagneticemissions due to operation of the module. The insert 20 is provided witha matrix of openings 22 as seen in FIG. 1B, and is installed by aligningthe openings 22 with the terminals 12, and pushing the insert 20 ontothe terminal matrix. An encapsulating material 24 is injected into theregion between the circuit board 18 and the insulator block 14 as shownin FIG. 1A for improved environmental sealing.

The filter insert 20 can be formed on a circuit board, on a rigidplastic substrate or on a flexible substrate. In cases where the insertis formed on a circuit board or a rigid plastic substrate, the terminals12 can be soldered to metallic pads adjacent to the openings 22, or theopenings 22 can be through-plated with metal so that a reliableelectrical connection is established by virtue of an interference fitbetween the terminals 12 and the through-plated metal. An interferencefit between the terminals 12 and the filter insert circuitry can also beachieved in cases where the insert 20 is formed on a flexible substrateby extending the circuit traces across the openings 22, leaving anopening that is smaller than the outline of a terminal 12. An example ofa filter insert formed on a plastic substrate with through-platedopenings is shown in the U.S. Pat. No. 6,413,119 to Gabrisko et al.,while an example of a filter insert formed on a flexible substrate isdisclosed in the U.S. Pat. No. 5,415,569 to Colleran et al.

Of the various filter insert designs discussed above, the flexiblecircuit approach is particularly attractive from a cost stand point,primarily because the interference fit electrical connections betweenthe connector terminals 12 and the filter insert 20 permits lowinsertion force (compared to the through-plated approach) and eliminatesthe expense of soldering and/or through-plating. However, reliabilitytesting has shown that when the module is subjected to extended thermalcycling, the thermal expansion and contraction of the encapsulatingmaterial 24 is transmitted to the flexible circuit, which in turn, leadsto fatigue-related failures of the solder joints and traces formed onthe circuit. Accordingly, what is needed is an improved filter inserthaving the low insertion force and low cost advantages of a flexiblecircuit, but with improved thermal cycle reliability.

SUMMARY OF THE INVENTION

The present invention is directed to an improved filter insert for aterminal connector, where the filter insert comprises a rigid substratefor good thermal cycle reliability and low-cost interference fitelectrical connections between the filter insert and the connectorterminals. In a first embodiment, the filter insert comprises a flexiblecircuit bonded to the rigid substrate, and the substrate is providedwith over-sized openings that the terminals pass through withoutinterference. A second embodiment is like the first, except that thefilter circuit traces are formed directly on the rigid substrate, andthe substrate material backing the terminal connection sites is removedto form the over-sized openings. The thermal bending stress applied tothe traces and solder joints of the filter insert of this invention isconsiderably reduced compared to the flexible circuit approach, and theinsertion force of the filter insert is essentially the same as with aflexible circuit due to the over-sized substrate openings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a prior art connector assemblyincluding a filter insert.

FIG. 1B is a elevation view of the filter insert depicted in FIG. 1A.

FIG. 2 is a cross-sectional view of a filter insert according to a firstembodiment of this invention.

FIG. 3 is a cross-sectional view of a filter insert according to asecond embodiment of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 2, the reference numeral 20′ generally designates afilter insert according to a first embodiment of this invention. In thisembodiment, the filter insert includes a rigid substrate 32, a flexiblefilm 34 adhesively bonded to the substrate 32, and an electrical filtercircuit including the copper traces 36 formed on the exposed surface ofthe film 34. The substrate 32 is preferably formed of FR4 printedcircuit board, but can be any rigid material having a coefficient ofthermal expansion that closely matches that of the copper traces 36. Theflexible film is preferably formed of polyimide, but can be any flexiblematerial having a coefficient of thermal expansion that closely matchesthat of the copper traces 36. In addition to the traces 36, the filtercircuit includes filter elements such as the capacitor 38, illustratedas a surface mount device attached to the trace segments 36 a and 36 bby the solder joints 40. In a typical implementation, the capacitors 38form part of a filter network for low-pass filtering electrical signalscarried by the connector terminals 12.

The openings 22 a′, 22 b′ in the filter circuit 20′ are formed byconcentric openings 42, 44, 46 in the substrate 32, the flexible circuit34 and the copper traces 36, as best seen in reference to the opening 22a′. The openings 42 and 44 are over-sized relative to the connectorterminals 12, and offer no resistance to the terminals 12 when thefilter insert 20′ is installed on the terminal matrix. In contrast, theopening 46 in the copper trace 36 is under-sized relative to theterminals 12. As indicated at the opening 22 b′, the terminals 12 deformthe copper trace material 36 c adjacent to the openings 46 as the filterinsert 20′ is installed on the terminal matrix, forming an interferenceelectrical connection between the terminals 12 and the copper tracesegments defining the openings 46. The cumulative resistance offered bythe various openings 46 to the installation of filter insert 20′ isrelatively small, and virtually identical to that of the prior artflexible circuit filter insert. In usage, mechanical stresses due toexpansion and contraction of the encapsulating material 24 duringthermal cycling of the module are borne by the rigid substrate 32,drastically reducing the stress borne by the circuit traces 36 andsolder joints 40 as compared to the prior art flexible circuit filterinsert. Consequently, the reliability of the filter insert 20′ issignificantly improved compared to that of the prior art flexiblecircuit filter insert.

FIG. 3 depicts a filter insert 20″ according to a second embodiment ofthis invention. The filter insert 20″ is like the filter insert 20′,except that the copper traces 36 are formed directly on the rigidsubstrate 32. In this case, the openings 22 a″ and 22 b″ are defined bytwo concentric openings: the opening 42 in the substrate 32 and theopening 46 in the copper trace material 36 c. Thus the filter insert 20″provides the same low insertion force and high thermal cycle reliabilityas the filter insert 20′, but at a reduced cost due to the eliminationof the flexible film 34 and the adhesive for bonding the film 34 to thesubstrate 32.

The filter inserts 20′ and 20″ may be easily manufactured usingconventional printed circuit processing techniques, as will beappreciated by those skilled in the art. In regard to the filter insertopenings, the copper trace openings 46 may be formed by photo-etching,the flexible film openings 44 may be formed by selective etchingfollowing formation of the circuit traces 36, and the substrate openings42 may be formed by drilling.

In summary, the present invention provides a reliable, low insertionforce and low-cost filter insert for usage in conjunction withelectrical connectors for the purpose of attenuating unwanted electricalnoise and reducing radiated electromagnetic emissions. While the filterinsert of this invention has been described in reference to theillustrated embodiments, it is anticipated that various modifications inaddition to those mentioned above will occur to those skilled in theart. In this regard, it should be understood that filter insertsincluding these and other modifications may fall within the scope ofthis invention, which is defined by the appended claims.

1. A filter insert for insertion on at least one electrical terminal ina connector assembly, the filter insert comprising: a rigid substratehaving a first opening through which said electrical initially passeswhen said filter is inserted on said electrical terminal, said firstopening being over-sized relative to said electrical terminal so thatsaid electrical terminal passes through said first opening withoutinterference; and filter circuitry for filtering electrical signalscarried by said electrical terminal, including at least one conductortrace having a coefficient of thermal expansion substantially equal to acoefficient of thermal expansion of said rigid substrate, said conductortrace being formed on a flexible film bonded to a surface of said rigidsubstrate facing away from said connector assembly, said conductor tracealso having a second opening that is concentric with said first openingand aligned with concentric openings in said flexible film, said secondopening being under-sized relative to said electrical terminal so thatsaid conductor trace deforms away from said rigid substrate when saidelectrical passes through said second opening, forming interference fitelectrical connections between said conductor trace and said electricalterminal.
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